During the semiconductor device fabrication process, high speed, low resolution wafer inspections (e.g., Bright Field, Dark Field, etc.) are performed on selected wafers from a fabrication lot. Generally, these inspections report a number of defects on the wafers within the lot. Out of the reported detects, a small subset (e.g., a sub-sample) of the defects are selected for review and defect-type classification. Classification can be done by capturing a high-resolution image of each sampled defect, examining the image to determine the type of defect present, then assigning an appropriate classification code to the defect. High-resolution images of wafer defects can be captured using techniques such as scanning electron microscopy (Defect-Review SEM tools), electron-beam scanning (E-Beam tools), etc. of areas of one or more die on certain wafers. The captured images can then be selectively reviewed to classify the type of defect present in those images.
Additionally, relatively large portions of one or more die on selected wafers can be directly imaged in high resolution using techniques such as electron-beam scanning (E-Beam), without first resorting to a low resolution (high speed) inspection process (e.g. Bright Field or Dark Field). Although considerably slower than low resolution inspection systems, this produces a set of high resolution image files, possibly covering a larger area than Review SEM images.
Existing image review and classification methods are designed to classify a defect that occupies a small subarea of the image. Due to the diversity of features in an image and the large volume of images being generated, it can be challenging to evaluate and examine anomalies that may be present.